1. Field of the Invention
The field of the invention is disconnect switches and circuit breaker mechanisms used in industrial power distribution circuits.
2. Description of the Prior Art
Manually operated disconnect switches are used in plant distribution lines that feed industrial loads. Such switches are characterized by their ratings which typically range from 30 amperes to 400 amperes. Larger current carrying capacities require proportionally larger contacts and terminals, and greater spacing is required between such contacts or terminals and any other conducting portions of the switch supporting structure. On the other hand, appreciable amounts of heat are generated in the switch contacts and terminals and this heat must be dissipated at a reasonable rate. Thus, the construction of the insulating portions of the switch structure must provide electrical insulation without high heat retention.
Zaffrann, U.S. Pat. No. 4,251,700, issued Feb. 17, 1981, entitled "Disconnect Switch," and assigned to the assignee of the present invention, discloses a multi-pole manual disconnect switch rated at 200 amperes. Each pole has a load-side stationary contact that is continuously engaged by a pair of arcuate contact blades. The blades are carried by a crossbar, which when pivoted to its closed position carries the blades into contact with a line-side stationary contact. The load-side and line-side stationary contacts are spaced apart and are connected to respective terminals that are mounted on a base of insulating material.
This construction cannot be adapted to higher current ratings, such as 400 amperes, due to the increase in size required for the stationary contacts and terminals on the line-side and the heat retention that results from such contacts and terminals being mounted on the insulating base provided in the prior disconnect switch.
Besides these considerations, there is also a need to improve the manner of assembling the stationary contact module, which in the prior construction could not be conveniently removed without first removing the contact carrying crossbar.